Various devices have been suggested in the past for augmenting the lift on an aircraft either to reduce the required wing area or to decrease the required forward speed of the aircraft during take-off and landing. Such devices have not enjoyed widespread success due primarily to the fact that such devices have had difficulty in providing adequate control over the aircraft at low speed, especially when vertical take-offs and landings were attempted. One type of suggested lift augmenting device uses rotors positioned in the wings. Examples of this type of lift augmenting device are shown in U.S. Pat. Nos. 2,344,515 and 3,065,928. These rotors are fixed vanes in the rotors making it difficult to vary the flow of air through the rotors.